Driver assistance systems in vehicles often use a camera to scan or image or detect the surroundings of the vehicle, for example in order to detect various kinds of objects in the area around the vehicle. As a rule, the camera is arranged behind the windshield of the vehicle and looks through the windshield in the direction of travel. Examples are vehicle cameras for the detection of road surface markings, night vision cameras or stereo cameras used as optical distance sensors. Typically, additional sensors for rain detection or sensors designed to detect the lighting conditions are located next to the installation space of such a camera system.
For example, DE 103 55 205 A1 discloses a device for mounting a camera module behind a windshield in a vehicle, wherein a camera module designed to record images of the area ahead of the vehicle is arranged in a first installation space behind the windshield. A second installation space for a rain sensor, whose sensor surface also faces the windshield, is provided underneath the installation space for the camera module.
The device described in DE 103 55 205 A1 as well as other known devices where several sensors, in particular camera modules and rain or light sensors, are arranged behind a windshield of a vehicle have the drawback that each camera module and each sensor unit needs its own area of view through the windshield, so that they require much installation space, which is available only to a limited extent.
There have been attempts to combine several sensor functions in one camera module, for example by using bifocal or multifocal camera modules, i.e. cameras that are able to record images from a far range and a near range on a single image recording element. Such a system is known, for example, from EP 1 923 280 A1. An additional optical element including a positive lens (convex lens) enables an existing imaging system, which is focused on a far range of vision, to project an additional clear image of objects from a near range of vision, in this case raindrops on a windshield, on to an image recording element. When there are no raindrops on the windshield, the image projected on to the image recording element is exclusively dominated by the far range of vision. When there are drops on the windshield, the near-range image will be superimposed on the far-range image in the same image plane, modifying the generated image signal.
The system described in EP 1 923 280 A1 as well as other multifocal imaging systems from the state of the art have the drawback that radiation from a near range of vision as well as from a far range of vision is incident, and generates an image signal, on a shared area of the image recording element at the same time. Due to the radiation from both monitoring areas being superimposed on each other, the image quality decreases for both driver assistance functions, i.e. far-range monitoring and near-range monitoring.